1. Field of the Invention
This invention relates to a signal processing device suitably employed in a still picture imaging device. More particularly, it relates to a signal processing device that is able to perform particularly efficiently signal processing, a control method therefor, an imaging device and a recording/reproducing apparatus.
2. Description of the Related Art
A digital still camera retrieves image data obtained by a CCD image sensor into a DRAM or a flash memory and subsequently transfers the image data to a so-called personal computer or the like. A major proportion of this type of the digital still camera has so far been of the type coping with the video graphics array (VGA) system.
Referring to FIG. 1, this digital still camera 200 includes a CCD image sensor 201 for generating image signals, an input processing/image processing circuit 202, a memory controller 203 for reading and writing image data, an output processing circuit 204 for conversion to an output image of a pre-set system, a finder 205 for displaying the state of an object at the time of image shooting, a recording unit 207 for recording compressed image data over a CPU bus 206 and a compression/expansion circuit 208 for compressing/expanding image data. The digital still camera 200 also includes a memory 209, formed by, for example, a DRAM, and a CPU 210 for controlling the overall device.
Before starting the image shooting of an object, the user has to confirm an object image displayed on the finder 205. This state is termed a finder mode. At this time, the CCD image sensor 201 sends image signals obtained on photoelectric conversion to the input processing/image processing circuit 202. The input processing/image processing circuit 202 performs the correlated dual sampling processing on the image signals to digitize the image signals. The input processing/image processing circuit 202 then performs pre-set signal processing, such as gamma correction, knee processing or camera processing and routes the processed image signals to the memory controller 203, which then is responsive to the control by the CPU 210 to send the image data from the input processing/image processing circuit 202 to the output processing circuit 204. The output processing circuit 204 encodes image data in accordance with, for example, the National Television System Committee (NTSC) system, and analogizes the encoded image data to route the resulting analog data to the finder 205. This allows the object as an object of image shooting to be indicated on the finder 205.
On the other hand, if the user pushes a shutter button, not shown, to shift to the recording mode, the memory controller 203 causes the image data furnished from the input processing/image processing circuit 202 to be written in the memory 209. The CPU 210 causes the image data to be read out from the memory 209 and compresses the image data from the recording unit 207 in the compression/expansion circuit 208 with compression in accordance with, for example, the Joint photographic Experts Group (JPEG) system to record the compressed image data in the recording unit 207.
If the user performs pre-set processing to shift to the reproducing mode, the CPU 210 causes image data to be read out from the recording unit 207 to cause the image data to be expanded in JPEG system in the compression/expansion circuit 208 to route the resulting data via memory controller 203 and output processing circuit 204 to the finder 205. This causes the as-shot image to be displayed on the finder 205.
In keeping up with recent outstanding technical progress in the CCD image sensor, the resolution of image data is nearly surpassing 1,000,000 pixels. On the other hand, it may be feared that the digital still camera of the above-described structure cannot sufficiently cope with the image data exceeding 1,000,000 pixels.
If, for example, the CCD image sensor 201 outputs image signals of high resolution, the input processing/image processing circuit 202, memory controller 203 or the output processing circuit 204 cannot process image data in real-time, such that the delay of, for example, one second is liable to be produced until an image of the object is displayed on the finder 205. This incurs an inconvenience in shooting an image of object even if the object makes the slightest movement.
Moreover, since the accessing to image data which needs to be in real-time and data accessing by the CPU 210 with indefinite data rate are performed on a common bus, the real-time accessing is difficult to realize if the image data is increased in volume, thus causing the CPU bus to be stagnant to lower the processing ability of the respective circuits.